1 | /* SPDX-License-Identifier: GPL-2.0 */ |
2 | /* rwsem.h: R/W semaphores, public interface |
3 | * |
4 | * Written by David Howells (dhowells@redhat.com). |
5 | * Derived from asm-i386/semaphore.h |
6 | */ |
7 | |
8 | #ifndef _LINUX_RWSEM_H |
9 | #define _LINUX_RWSEM_H |
10 | |
11 | #include <linux/linkage.h> |
12 | |
13 | #include <linux/types.h> |
14 | #include <linux/list.h> |
15 | #include <linux/spinlock.h> |
16 | #include <linux/atomic.h> |
17 | #include <linux/err.h> |
18 | #include <linux/cleanup.h> |
19 | |
20 | #ifdef CONFIG_DEBUG_LOCK_ALLOC |
21 | # define __RWSEM_DEP_MAP_INIT(lockname) \ |
22 | .dep_map = { \ |
23 | .name = #lockname, \ |
24 | .wait_type_inner = LD_WAIT_SLEEP, \ |
25 | }, |
26 | #else |
27 | # define __RWSEM_DEP_MAP_INIT(lockname) |
28 | #endif |
29 | |
30 | #ifndef CONFIG_PREEMPT_RT |
31 | |
32 | #ifdef CONFIG_RWSEM_SPIN_ON_OWNER |
33 | #include <linux/osq_lock.h> |
34 | #endif |
35 | |
36 | /* |
37 | * For an uncontended rwsem, count and owner are the only fields a task |
38 | * needs to touch when acquiring the rwsem. So they are put next to each |
39 | * other to increase the chance that they will share the same cacheline. |
40 | * |
41 | * In a contended rwsem, the owner is likely the most frequently accessed |
42 | * field in the structure as the optimistic waiter that holds the osq lock |
43 | * will spin on owner. For an embedded rwsem, other hot fields in the |
44 | * containing structure should be moved further away from the rwsem to |
45 | * reduce the chance that they will share the same cacheline causing |
46 | * cacheline bouncing problem. |
47 | */ |
48 | struct rw_semaphore { |
49 | atomic_long_t count; |
50 | /* |
51 | * Write owner or one of the read owners as well flags regarding |
52 | * the current state of the rwsem. Can be used as a speculative |
53 | * check to see if the write owner is running on the cpu. |
54 | */ |
55 | atomic_long_t owner; |
56 | #ifdef CONFIG_RWSEM_SPIN_ON_OWNER |
57 | struct optimistic_spin_queue osq; /* spinner MCS lock */ |
58 | #endif |
59 | raw_spinlock_t wait_lock; |
60 | struct list_head wait_list; |
61 | #ifdef CONFIG_DEBUG_RWSEMS |
62 | void *magic; |
63 | #endif |
64 | #ifdef CONFIG_DEBUG_LOCK_ALLOC |
65 | struct lockdep_map dep_map; |
66 | #endif |
67 | }; |
68 | |
69 | /* In all implementations count != 0 means locked */ |
70 | static inline int rwsem_is_locked(struct rw_semaphore *sem) |
71 | { |
72 | return atomic_long_read(v: &sem->count) != 0; |
73 | } |
74 | |
75 | #define RWSEM_UNLOCKED_VALUE 0L |
76 | #define __RWSEM_COUNT_INIT(name) .count = ATOMIC_LONG_INIT(RWSEM_UNLOCKED_VALUE) |
77 | |
78 | /* Common initializer macros and functions */ |
79 | |
80 | #ifdef CONFIG_DEBUG_RWSEMS |
81 | # define __RWSEM_DEBUG_INIT(lockname) .magic = &lockname, |
82 | #else |
83 | # define __RWSEM_DEBUG_INIT(lockname) |
84 | #endif |
85 | |
86 | #ifdef CONFIG_RWSEM_SPIN_ON_OWNER |
87 | #define __RWSEM_OPT_INIT(lockname) .osq = OSQ_LOCK_UNLOCKED, |
88 | #else |
89 | #define __RWSEM_OPT_INIT(lockname) |
90 | #endif |
91 | |
92 | #define __RWSEM_INITIALIZER(name) \ |
93 | { __RWSEM_COUNT_INIT(name), \ |
94 | .owner = ATOMIC_LONG_INIT(0), \ |
95 | __RWSEM_OPT_INIT(name) \ |
96 | .wait_lock = __RAW_SPIN_LOCK_UNLOCKED(name.wait_lock),\ |
97 | .wait_list = LIST_HEAD_INIT((name).wait_list), \ |
98 | __RWSEM_DEBUG_INIT(name) \ |
99 | __RWSEM_DEP_MAP_INIT(name) } |
100 | |
101 | #define DECLARE_RWSEM(name) \ |
102 | struct rw_semaphore name = __RWSEM_INITIALIZER(name) |
103 | |
104 | extern void __init_rwsem(struct rw_semaphore *sem, const char *name, |
105 | struct lock_class_key *key); |
106 | |
107 | #define init_rwsem(sem) \ |
108 | do { \ |
109 | static struct lock_class_key __key; \ |
110 | \ |
111 | __init_rwsem((sem), #sem, &__key); \ |
112 | } while (0) |
113 | |
114 | /* |
115 | * This is the same regardless of which rwsem implementation that is being used. |
116 | * It is just a heuristic meant to be called by somebody already holding the |
117 | * rwsem to see if somebody from an incompatible type is wanting access to the |
118 | * lock. |
119 | */ |
120 | static inline int rwsem_is_contended(struct rw_semaphore *sem) |
121 | { |
122 | return !list_empty(head: &sem->wait_list); |
123 | } |
124 | |
125 | #else /* !CONFIG_PREEMPT_RT */ |
126 | |
127 | #include <linux/rwbase_rt.h> |
128 | |
129 | struct rw_semaphore { |
130 | struct rwbase_rt rwbase; |
131 | #ifdef CONFIG_DEBUG_LOCK_ALLOC |
132 | struct lockdep_map dep_map; |
133 | #endif |
134 | }; |
135 | |
136 | #define __RWSEM_INITIALIZER(name) \ |
137 | { \ |
138 | .rwbase = __RWBASE_INITIALIZER(name), \ |
139 | __RWSEM_DEP_MAP_INIT(name) \ |
140 | } |
141 | |
142 | #define DECLARE_RWSEM(lockname) \ |
143 | struct rw_semaphore lockname = __RWSEM_INITIALIZER(lockname) |
144 | |
145 | extern void __init_rwsem(struct rw_semaphore *rwsem, const char *name, |
146 | struct lock_class_key *key); |
147 | |
148 | #define init_rwsem(sem) \ |
149 | do { \ |
150 | static struct lock_class_key __key; \ |
151 | \ |
152 | __init_rwsem((sem), #sem, &__key); \ |
153 | } while (0) |
154 | |
155 | static __always_inline int rwsem_is_locked(struct rw_semaphore *sem) |
156 | { |
157 | return rw_base_is_locked(&sem->rwbase); |
158 | } |
159 | |
160 | static __always_inline int rwsem_is_contended(struct rw_semaphore *sem) |
161 | { |
162 | return rw_base_is_contended(&sem->rwbase); |
163 | } |
164 | |
165 | #endif /* CONFIG_PREEMPT_RT */ |
166 | |
167 | /* |
168 | * The functions below are the same for all rwsem implementations including |
169 | * the RT specific variant. |
170 | */ |
171 | |
172 | /* |
173 | * lock for reading |
174 | */ |
175 | extern void down_read(struct rw_semaphore *sem); |
176 | extern int __must_check down_read_interruptible(struct rw_semaphore *sem); |
177 | extern int __must_check down_read_killable(struct rw_semaphore *sem); |
178 | |
179 | /* |
180 | * trylock for reading -- returns 1 if successful, 0 if contention |
181 | */ |
182 | extern int down_read_trylock(struct rw_semaphore *sem); |
183 | |
184 | /* |
185 | * lock for writing |
186 | */ |
187 | extern void down_write(struct rw_semaphore *sem); |
188 | extern int __must_check down_write_killable(struct rw_semaphore *sem); |
189 | |
190 | /* |
191 | * trylock for writing -- returns 1 if successful, 0 if contention |
192 | */ |
193 | extern int down_write_trylock(struct rw_semaphore *sem); |
194 | |
195 | /* |
196 | * release a read lock |
197 | */ |
198 | extern void up_read(struct rw_semaphore *sem); |
199 | |
200 | /* |
201 | * release a write lock |
202 | */ |
203 | extern void up_write(struct rw_semaphore *sem); |
204 | |
205 | DEFINE_GUARD(rwsem_read, struct rw_semaphore *, down_read(_T), up_read(_T)) |
206 | DEFINE_GUARD(rwsem_write, struct rw_semaphore *, down_write(_T), up_write(_T)) |
207 | |
208 | DEFINE_FREE(up_read, struct rw_semaphore *, if (_T) up_read(_T)) |
209 | DEFINE_FREE(up_write, struct rw_semaphore *, if (_T) up_write(_T)) |
210 | |
211 | |
212 | /* |
213 | * downgrade write lock to read lock |
214 | */ |
215 | extern void downgrade_write(struct rw_semaphore *sem); |
216 | |
217 | #ifdef CONFIG_DEBUG_LOCK_ALLOC |
218 | /* |
219 | * nested locking. NOTE: rwsems are not allowed to recurse |
220 | * (which occurs if the same task tries to acquire the same |
221 | * lock instance multiple times), but multiple locks of the |
222 | * same lock class might be taken, if the order of the locks |
223 | * is always the same. This ordering rule can be expressed |
224 | * to lockdep via the _nested() APIs, but enumerating the |
225 | * subclasses that are used. (If the nesting relationship is |
226 | * static then another method for expressing nested locking is |
227 | * the explicit definition of lock class keys and the use of |
228 | * lockdep_set_class() at lock initialization time. |
229 | * See Documentation/locking/lockdep-design.rst for more details.) |
230 | */ |
231 | extern void down_read_nested(struct rw_semaphore *sem, int subclass); |
232 | extern int __must_check down_read_killable_nested(struct rw_semaphore *sem, int subclass); |
233 | extern void down_write_nested(struct rw_semaphore *sem, int subclass); |
234 | extern int down_write_killable_nested(struct rw_semaphore *sem, int subclass); |
235 | extern void _down_write_nest_lock(struct rw_semaphore *sem, struct lockdep_map *nest_lock); |
236 | |
237 | # define down_write_nest_lock(sem, nest_lock) \ |
238 | do { \ |
239 | typecheck(struct lockdep_map *, &(nest_lock)->dep_map); \ |
240 | _down_write_nest_lock(sem, &(nest_lock)->dep_map); \ |
241 | } while (0) |
242 | |
243 | /* |
244 | * Take/release a lock when not the owner will release it. |
245 | * |
246 | * [ This API should be avoided as much as possible - the |
247 | * proper abstraction for this case is completions. ] |
248 | */ |
249 | extern void down_read_non_owner(struct rw_semaphore *sem); |
250 | extern void up_read_non_owner(struct rw_semaphore *sem); |
251 | #else |
252 | # define down_read_nested(sem, subclass) down_read(sem) |
253 | # define down_read_killable_nested(sem, subclass) down_read_killable(sem) |
254 | # define down_write_nest_lock(sem, nest_lock) down_write(sem) |
255 | # define down_write_nested(sem, subclass) down_write(sem) |
256 | # define down_write_killable_nested(sem, subclass) down_write_killable(sem) |
257 | # define down_read_non_owner(sem) down_read(sem) |
258 | # define up_read_non_owner(sem) up_read(sem) |
259 | #endif |
260 | |
261 | #endif /* _LINUX_RWSEM_H */ |
262 | |